In order to find a correspondence between the sonographic findings of endoscopic ultrasonography (EUS) and the histology of gastric myogenic tumors, histologic specimens (24 cases) and preoperative ultrasonograms (10 cases) were examined. Histologically, the incidence of necrosis within the tumor was more frequent and the area of necrosis was larger in leiomyosarcoma than in leiomyoma. Liquefaction necrosis was observed only in leiomyosarcoma. By EUS, myogenic tumors originating from the proper muscle were delineated as clearly demarcated hypoechoic tumors arising from the fourth layer. Irregularly shaped sonolucent areas within the tumor corresponded to liquefaction necrosis. Thus, sonolucent areas may be indicative of leiomyosarcoma.